A thread of mercury of 10.2 g is in a tube of uniform cross section 0.1cm ^{3} . Calculate the length of thread. The density of mercury is 13.6g/cm ^{3}

we know that

density = mass / volume

or

d = m / V

here

d = 13.6 gm/cm^{3}

m = 10 gm

and V = πr^{2}.l = A.l

where A is the area of cross-section = 0.1 cm^{2} and l is the length

thus, we have

13.6 = 10 / (A.l)

or

l = 10 / (13.6 x A) = 10 / (13.6 x 0.1)

or

l = 10 / 1.36

thus, the length of the tube will be

**l = 7.352 cm**

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